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into the infective L3 stage that, when ingested by a suitable host, develops into ostertagi L4, L5 and eventually adult . While Ostertagia can become patent within 21 days of ingestion, stage four larvae can immunology and undergo maturation arrest in the mucosa and re-emerge en masse at a later date. This phenomenon is more common when L3 larvae are exposed to cool temperatures implications for and in regions with regular dry seasons. Ostertagia infection can result in two syndromes. Type I disease affects diagnosis calves in the summer and autumn and is characterised by diarrhoea and ill-thrift. In type II disease, the arrested larvae Genevieve D’Amours of SVS Laboratories discusses mature suddenly, causing severe damage to the abomasum as they emerge in the ins and outs of the abomasal parasite Ostertagia nine-month-old to one-year-old or older ostertagi, including diagnostic options. . This can result in sudden severe illness and even death. Type II disease is uncommon in New Zealand. OSTERTAGIA IS A gastrointestinal These changes lead to an increase in pH parasite of cattle that causes significant and decreased conversion of pepsinogen IMMUNITY economic losses to the and beef to pepsin, which causes decreased The innate immune response is involved industries. It is a that dwells protein absorption, intestinal bacteria initially, with neutrophils being present in the mucus of the abomasal glands overgrowth and diarrhoea. and induces a mucosal inflammatory Ostertagia eggs are shed in faeces and reaction and hyperplasia and metaplasia develop into free-living L1 and L2 larvae of the mucus neck cells (Figure 1). on the pasture. The larvae then develop FIGURE 1: Abomasal mucosa with mucus neck cell metaplasia and hyperplasia and nematodes.

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FIGURE 2: Ostertagia larvae surrounded by degenerate neutrophils.

FIGURE 3: Lymphoid nodule within abomasal mucosa.

immunity, which is characterised by resistance to reinfection, can take 18 months or more of continuous exposure to develop. Parasite burdens can be seen in older than one year and after stressful periods such as parturition and early lactation. The mechanisms contributing to resistance to reinfection are still poorly understood, but decreased worm fecundity is thought to be an early in the abomasum soon after infection. lymphadenopathy and increased numbers manifestation of protective immunity. Neutrophils are recruited to the site of parasite-specific lymphocytes within In calves it is thought that increased quickly after infection (Figure 2). the lymph nodes and abomasal mucosa IgA levels in the abomasal mucosa may Neutrophils have been shown to be (Figure 3). Immunity to parasites typically regulate worm fecundity. In , able to release neutrophil extracellular involves a Th2 response mediated by the the presence of IgA directed against traps (NETs). These consist of a mesh release of several interleukins (IL4, IL5, carbohydrate larval surface antigen of chromatin strands and protein IL10 and IL13) and IgE, which attract (CarLA) has been associated with granules containing myeloperoxidase and mast cells, eosinophils and basophils. immunity to parasites, with resulting neutrophil elastase, which can trap and Histologically, there are increased decreased faecal egg counts (FECs) kill some microbes. Ostertagia extract numbers of eosinophils, mast cells and and increased weight gains. Salivary and live L4 larvae have been shown to globule leukocytes, which are thought anti-CarLA IgA assays are being used to also induce formation of NETs in vitro to originate from mast cells, within the select sheep with increased resistance to (Mendez et al, 2018). abomasal mucosa (Figures 4, 5). Ostertagia parasites for breeding. A study looking Infections with Ostertagia also illicit a infections also trigger a Th1 response, at anti-CarLA salivary IgA in first season humoral response, with immunoglobulins which is usually most effective against grazing heifers found that IgA levels being detected in the serum and mucus intracellular pathogens, with upregulation were negatively correlated with FECs of infected animals. Ostertagia antigens of interferon gamma (IFN-γ). but not with pepsinogen levels, total are presented to the draining lymph Compared to other parasites, the serum Ostertagia immunoglobulins nodes soon after infection, and calves immune response to Ostertagia is or daily weight gain, and therefore quickly mount a response resulting in usually slow and incomplete. Protective concluded that salivary IgA levels did

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FIGURE 4: Infiltration of lymphocytes and eosinophils within abomasal lamina propria.

FIGURE 5: Globule leukocytes within abomasal epithelium. not differentiate between immunity or exposure to the parasites (Merlin et al, 2017). More research is needed to elucidate the mechanisms of protective immunity in cattle.

DIAGNOSTIC OPTIONS FOR GASTROINTESTINAL NEMATODES FECs remain the most widely used tool for the detection of gastrointestinal parasites in cattle and other animals. Faecal larval cultures can then assess which types of parasite are present and what percentage of the nematodes are Ostertagia. However, FECs will not always correlate to abomasal damage, especially if large numbers of immature adequate to interpret mean serum a longer grazing period, percentage of larvae are present. This can be a pepsinogen (Charlier et al, 2011). animals with positive FECs, and BTM significant issue in type II ostertagiosis Serological assays have been Ostertagia ELISA, but not pepsinogen where there are large numbers of developed to look at antibody levels levels or individual serum ELISA hypobiotic larvae. against Ostertagia crude worm extract (Ravimet, 2014). In Argentina, where Serum pepsinogen can be used in serum, milk and bulk tank milk animals are grazed year round and may to detect abomasal damage caused (BTM)samples. In previous studies, be more representative of the New by Ostertagia, as the increased antibody levels measured by BTM Zealand systems, parasite burden in abomasal pH decreases conversion of enzyme-linked immunosorbent the first month post-partum is high. In pepsinogen to pepsin and increases assay (ELISA) have been negatively this region, milk production response serum pepsinogen. This test is a good correlated to milk yield, and have a to anthelminthic treatment in the first indicator of Ostertagia burden in positive association with increased month post-partum was correlated to young animals but not in adult cattle. milk yield following anthelminthic FECs but not with pepsinogen or milk Other diseases causing abomasal treatment. However, most of these Ostertagia ELISA (Mejía, 2011). This damage or increases in pH, including studies were performed in Europe and study also found that there was no abomasal displacement, can also North America, where animals are correlation between FEC and individual increase pepsinogen. housed for a significant proportion milk ELISA or pepsinogen. This suggests In first-season grazing calves, of the year. that BTM ELISA may provide a good sampling seven animals from groups In France, response to treatment indication of parasite exposure of the of up to 40 animals is considered with anthelminthic was correlated with group, especially in situations where

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determination in grazing dairy cattle in relation to parasite exposure may be low, and the REFERENCES: milk production. 183,174–7, response of a group to treatment. Charlier J, Dorny P, Levecke B, Demeler J, 2011 However, individual humoral response von Samson-Himmelstjerna G, Hoglund J, Mendez J, Sun D, Tuo W, Xiao Z. Bovine measured by serum or milk ELISA does Vercruysse J. Serum pepsinogen levels to monitor neutrophilis form extracellular traps in response to gastrointestinal nematode infections in cattle not appear to correlate with patent the gastrointestinal parasite Ostertagia ostertagi. revisited. Research in Veterinary Science 90, 451–6, Nature Scientific Reports 8, 17598, 2018 infections and response to treatment. 2011 Merlin A, Shaw R, Chauvain A, Bareille N, Control of ostertagiosis is still Forbes AB, Vercruysse J, Charlier J. A survey Chartier C. Significance of anti-CarLA salivary dependent on the use of anthelminthic. of the exposure to Ostertagia ostertagi in dairy IgA antibody in first season grazing cattle naturally With growing concerns for anthelminthic cow herds in Europe through the measurement infected with gastrointestinal nematodes. Veterinary of antibodies in milk samples from bulk tank. Parasitology 243, 36–41, 2017 resistance, targeted treatment has been Veterinary Parasitology 157, 100–7, 2008. suggested as a method to mitigate the Mihi B, Van Meulder F, Vancoppernolle S, Jackson A, Ellis KA, McGoldrick J, Jonsson Rinaldi M. Ven Der Broeck W, Godderis BM, risks. However, this requires selecting NN, Steer MJ, Forbes AB. Targeted anthelminthic Vercruysse J, Claerebout E, Geldhof P. Parasite animals most likely to respond to treatment of parasitic gastroenteritis in first grazing Immunology 36, 150–6, 2014 season dairy calves using daily live weight gain as an treatment, which may not always indicator. Veterinary Parasitology 244, 85–90, 2017 Ravimet N, Bareille N, Lehebel A, Ponnau be straightforward given the assay A, Chartier C, Chauvin A. Changes in milk McNeilly TN, Nisbet AJ. Immune modulation by limitations. In young animals, FECs and production after treatment against gastrointestinal helminth parasites of : Implications for nematodes according to parasitological and serum pepsinogens are the best options. In vaccine development and host immune competence. production-based indicators in adult dairy cows. adult animals, however, BTM Ostertagia Parasite 21, 52, 2015 Veterinary Parasitology 201, 95–109, 2014 ELISA will give a general indication of herd Mejía ME, Perri AF, Lincoff N, Miglierina Sekiya M, Zintl A, Doherty ML. Bulk milk exposure, and FEC in times of stress may MM, Cseh S, Ornstein AM, Becu-Villabolos ELISA and the diagnosis of parasite infections D, Lacau-Mengido IM. Comparison of three in dairy herds: A review. Irish Veterinary Journal help identify the most affected animals. methods for gastrointestinal nematode diagnosis 66(14), 2013